This invention relates generally to systems for detecting exiting passengers on public conveyances and specifically to systems using sonar for detecting the presence of passengers at exits of public conveyances, such as buses or trolley-buses.
At the present time, floormats with micro-switches are in prevalent use to detect the fact that a passenger is at the exit of a bus or trolley-bus. The operation of the micro-switch opens the exit doors for the passengers to leave when the vehicle is brought to a stop. Although the micro-switches will operate to open the door for the exiting passengers, the use of floormats with micro-switches leaves much to be desired. The switches often corrode due to moisture accumulating under the floormats. When the floormats are damaged or the micro-switches cease to operate properly, it is a tedious job to change the floormat and the micro-switch. In order to change the floormat and remove the damaged micro-switch, the doors must be removed, which in some cases necessitates the effort of two people for nine hours. Thus, not only is the repair procedure expensive and time consuming but the vehicle is out of service for an extended period of time.
Generally, other types of devices to detect passengers such as motion detectors are not basically applicable because passengers are stationary while waiting for the door to open. Motion detectors also suffer from vibration and electrical noise within the vehicle will often set off these detectors in the absence of passengers that are exiting. Presence or capacitor types of detector or electric eye, photocell systems are also not suitable because the doors when open are positioned within the stairwell.
This invention enables the use of sonar devices for in a system for detecting exiting passengers in public conveyances which does not have the shortcomings of existing systems as described above.